There is substantial evidence suggesting that the macrophage/monocyte serves as a reservoir for HIV infection and plays an important role in the pathogenesis of AIDS. HIV-1 replication is regulated by virally encoded proteins, as well as by cellular transcriptional factors. To understand the mechanisms of viral latency and restricted low level expression we have developed HIV infected monocytic cell lines, THP-1 as a model system where expression is observed at various levels; a. complete latency, b. restricted low level expression, and c. productive infection. In vitro transcription and DNA binding gel retardation assays have been devised to study the molecular mechanism of HIV gene regulation in monocytes/macrophages. Preliminary results showed the existence of negative regulatory factor(s) in the restricted state of HIV-infected THP-1. We are currently studying the DNA element(s) involved in the negative regulation of HIV expression. Using Southwestern screening technique, we have cloned cDNAs encoding for the proteins that bind to the negative regulatory element (NRE) of the HIV-LTR. The availability of the cDNA clones will make it possible to pursue structure function studies of the transcription factors involved in HIV gene expression. Modulation of transcription activity could serve as a potential target for AIDS therapy intervention. With regard to the roles of NF-kappa B in HIV gene expression, we have used purified NF-kappa B and demonstrated the involvement of the 65 + 50 kDa NF-kappa B heterotetramer in the negative regulation of HIV expression in monocytes. The protein, I(kappa)B, has been shown to be an inhibitor of NF-kappa B binding activity. I(kappa)B binds specifically to the 65 kDa subunit of NF-kappa B, blocks heterotetramer formation and rapidly dissociates the complex of NF-kappa B with its cognate DNA. Studies are in progress to prove that I(kappa)B is an inhibitor involved in this negative regulation of HIV transcription.